Shell deformations in the Baltic clam Macoma balthica from southern Baltic Sea (the Gulf of Gdansk): hypotheses on environmental effects

Live and Live-Dead Intraspecific Morphometric Comparisons as Proxies for Seagrass Stability in Conservation Paleobiology

Comparisons of life and death assemblages are commonly conducted to detect environmental change, including when historical records of live occurrences are unavailable. Most live-dead comparisons focus on assemblage composition, but morphology can also vary in species with environmental variables. Although live-dead morphologic comparisons are less explored, their data could be useful as a proxy in conservation paleobiology. We tested the potential for geometric morphometric data from live-and dead-articulated Stewartia floridana (Bivalvia: Lucinidae) to serve as proxies for seagrass occurrence and stability. The study area is at the northern end of Pine Island in Charlotte Harbor, FL, United States, an estuarine system with substantial seagrass loss in the 20th century and subsequent partial recovery. The area sampled has had relatively stable seagrass occurrences since at least the early 2000s. Live and dead-articulated S. floridana samples were collected from two transects through a patchy seagrass meadow, with sampled sites ranging from bare sand to 100% seagrass cover. Dead-articulated specimens were also collected from three adjacent transects. Live S. floridana shape covaried significantly with seagrass taxonomic composition and percent cover at the time of collection based on two-block partial least squares analysis, although shape differences between seagrass end members (100% Halodule wrightii and 100% Syringodium filiforme) were not significant by multivariate analysis of variance (MANOVA). Instead, specimens from 100% H. wrightii had significantly greater Procrustes variance. Live S. floridana shape data placed in categories describing seagrass stability over 6 years prior to sampling (and reflecting sclerochronologic estimates of maximum longevity) differed significantly based on MANOVA. For live and dead S. floridana from the same transects, shape differed significantly, but allometric trends did not. In addition, patterns of morphologic variation tied to seagrass stability were detected in dead-articulated valve shape. Dead shells from adjacent transects differed significantly in shape and allometric trend from both live and dead specimens collected together. We infer that morphometric differences recorded fine-scale spatial and temporal patterns possibly tied to environmental change. Therefore, geometric morphometrics may be a powerful tool that allows for death assemblages to track seagrass distributions through time prior to systematic monitoring, including in areas under high anthropogenic stress.

Identification of timing of scallop morphological deformity and mortality from shell oxygen isotope records

The Yesso scallop, Patinopecten yessoensis (Jay), is one of the most important bivalve species in the Japanese and Chinese mariculture industry. In recent years, however, high incidences of scallop shell deformity and mortality have occurred with increasing frequency, but timing of onset and underlying causes are often unclear. Here, we proposed a promising δ¹⁸O_shell-based method for constraining the onset of shell deformity and mortality of P. yessoensis. Following six months of intermediate suspension culture in Funka Bay, Northern Japan, shells from healthy, deformed and dead scallops were randomly sampled. High-resolution seawater temperature time-series computed from healthy scallop shell δ¹⁸O profiles were precisely and temporally aligned to the instrumental temperature curve, thus allowing δ¹⁸O_shell-derived temperature time-series from deformed and dead scallops to be contextualized and allowing timing of scallop deformity and death to be retrieved. Irrespective of scallop shell length, onsets of deformity were anchored in February, and since then deformed scallops grew slowly in comparison to healthy individuals. Without exception, however, dead scallops had already ceased their shell building and died before February, indicating different underlying causes of scallop deformity and mortality. Perhaps most promisingly, considering that shells do not have any isotopic turn-over and once formed, temperature information is locked in. Thus, this approach holds great promise for identifying time anchor points (onsets of deformity and death) in archived scallops collected over different time scales, especially during massive mortality events.

Historical shell form variation in Lottia subrugosa from southeast Brazilian coast: Possible responses to anthropogenic pressures

Mollusk shells can provide important information regarding environmental parameters. It is known that shell morphology is affected by both natural and anthropogenic factors. However, few studies have investigated alterations in shell morphology over a historical perspective and considering chemical contamination and climate changes. The present study assessed shell form (shape and size) variations of limpet (Lottia subrugosa) shells sampled from 1950 to 1981 (past) in comparison with organisms obtained in 2018 (present). Differences between shells from the past and present (2018) were detected, being shell weight and height the two most important affected parameters. The differences observed were attributed to the possible increase in contamination over the years due to human population growth and to climate change. Additionally, when shells from the past were evaluated according to the decade they were sampled, results indicate that it was necessary an interval of 40 years to shell form be altered within populations.

The effects of low seawater pH on energy storage and heat shock protein 70 expression in a bivalve Limecola balthica

Though biological consequences of CCS (Carbon Capture and Storage) implementation into the marine environment have received substantial research attention, the impact of potential CO₂ leakage on benthic infauna in the Baltic Sea remained poorly recognized. This study quantified medium-term (56-day laboratory exposure) effects of CO₂-induced seawater acidification (pH 7.7, 7.0 and 6.3) on energetic reserves and heat-shock protein HSP70 expression of adult bivalve Limecola balthica from the southern Baltic. While no clear impact was evident in the most acidic treatment (pH 6.3), moderate seawater hypercapnia (pH 7.0) induced elevated catabolism of high caloric reserves (carbohydrates including glycogen and lipids) in order to provide energy to cover enhanced metabolic requirements for acid-base regulation. Biochemical response did not involve, however, breakdown of proteins, suggesting that they were not utilized as metabolic substrates. As indicated also by subtle variations in the chaperone protein HSP70, the clams demonstrated high CO₂ tolerance, presumably through development of efficient defensive/compensatory mechanisms during their larval and/or ontogenic life stages.

Differing responses of the estuarine bivalve Limecola balthica to lowered water pH caused by potential CO2 leaks from a sub-seabed storage site in the Baltic Sea: An experimental study

Sub-Seabed CCS is regarded as a key technology for the reduction of CO₂ emissions, but little is known about the mechanisms through which leakages from storage sites impact benthic species. In this study, the biological responses of the infaunal bivalve Limecola balthica to CO₂-induced seawater acidification (pH7.7, 7.0, and 6.3) were quantified in 56-day mesocosm experiments. Increased water acidity caused changes in behavioral and physiological traits, but even the most acidic conditions did not prove to be fatal. In response to hypercapnia, the bivalves approached the sediment surface and increased respiration rates. Lower seawater pH reduced shell weight and growth, while it simultaneously increased soft tissue weight; this places L. balthica in a somewhat unique position among marine invertebrates.

Abnormalities in bivalve larvae from the Puck Bay (Gulf of Gdansk, southern Baltic Sea) as an indicator of environmental pollution

This study described the occurrence of abnormalities in bivalve larvae from the Puck Bay. Analyses of plankton samples collected in 2012-2013 showed that larval Mytilus trossulus, Mya arenaria, and Cerastoderma glaucum exhibited abnormalities that could indicate adverse environmental impacts. The deformities were mainly in shells, but missing soft tissue fragments and protruding vela were also noted. In addition to larval studies, we analyzed benthic postlarvae of Mytilus trossulus. Interestingly, grooves and notches at different locations of the prodissoconch, dissoconch, and shell margin were observed. Some of these deformations were reminiscent of the indentations found on the shell edge of larvae. Comparing the proportion of abnormal postlarvae to larvae with shell abnormalities suggested that the survival of larvae with shell abnormalities was low. Overall, our results suggested that the ratio of abnormal bivalve larvae could be used as an indicator of the biological effects of hazardous substances in the pelagic environment.

Covariations between Shell-Growth Parameters and the Control of the Ranges of Variation of Functionally Relevant Shell-Shape Parameters in Bivalves: A Theoretical Approach

Major traits of shell shape in bivalves may alternatively be described in terms of (i) functionally relevant parameters, assumed to play a significant role in the adaptation of bivalves molluscs to their environments (such as the shell-outline elongation E, ventral convexity K, and dissymmetry D), or (ii) growth-based parameters, directly controlled by the animal. Due to the geometrical linkage between functionally-relevant and growth-based parameters, adaptive constraints that may either widen or narrow the respective ranges of variations of the functional parameters lead to the onset of specific covariations (either positive or negative) between the growth-based parameters. This has practical interest since adaptive constraints are often difficult to identify directly, while they can be conveniently inferred indirectly via the easily recorded patterns of covariances between growth-based parameters. Hereafter, I provide the theoretical background of this tool, including (1) establishing the geometrical relationships between growth-based and functionally relevant parameters and (2) then specifying the correspondences between the different patterns of adaptive constraints, widening or narrowing the variations of the functional parameters and the corresponding patterns of covariations between the growth-based parameters. Illustrative examples of the practical use of this tool are provided, considering both interspecific and intraspecific variations within marine and fresh-water clams.

Bivalve mollusks in metal pollution studies: from bioaccumulation to biomonitoring

Contemporary environmental challenges have emphasized the need to critically assess the use of bivalve mollusks in chemical monitoring (identification and quantification of pollutants) and biomonitoring (estimation of environmental quality). Many authors, however, have considered these approaches within a single context, i.e., as a means of chemical (e.g. metal) monitoring. Bivalves are able to accumulate substantial amounts of metals from ambient water, but evidence for the drastic effects of accumulated metals (e.g. as a TBT-induced shell deformation and imposex) on the health of bivalves has not been documented. Metal bioaccumulation is a key tool in biomonitoring; bioavailability, bioaccumulation, and toxicity of various metals in relation to bivalves are described in some detail including the development of biodynamic metal bioaccumulation model. Measuring metal in the whole-body or the tissue of bivalves themselves does not accurately represent true contamination levels in the environment; these data are critical for our understanding of contaminant trends at sampling sites. Only rarely has metal bioaccumulation been considered in combination with data on metal concentrations in parts of the ecosystem, observation of biomarkers and environmental parameters. Sclerochemistry is in its infancy and cannot be reliably used to provide insights into the pollution history recorded in shells. Alteration processes and mineral crystallization on the inner shell surface are presented here as a perspective tool for environmental studies.

Bioindicative potential of shell abnormalities occurring in the clam Macoma balthica (L.) from the Baltic Sea

This study reports the occurrence of shell deformities in the Baltic clam Macoma balthica from the Northern Baltic Sea (Trösa Archipelago, Sweden). The functional significance and the bioindicative potential of observed exoskeleton' anomalies was assessed using a suite of physiological and morphological biomarkers. Analyzed shell deformations (SD) included damages of the dorsal margin visible as shell excavations, destruction of the beak, umbo and hinge ligament and decreased shell' transparency. Deformed clams exhibited worse physiological conditions and increased frequency of micronuclei. Skewed sex ratio towards male domination was observed in all studied populations. Spatial differences in the occurrence of deformed clams are reported, with more than 50% of deformed clams inhabiting polluted locations and 8% the reference station. These results are encouraging for the use of described SDs as initial and cost effective indicators of environmental health.